So-called strained-silicon techniques improve the performance of MOS field effect transistors by applying tensile or compressive stress to a channel region to enhance the charge carrier mobility. The mobility of electrons or holes in the channel region influences for example the on-resistance RDSon between source and drain in the conductive state of the transistor.
Strained silicon may be provided by epitaxial growth of silicon over a single crystal SiGe layer, wherein the silicon lattice is strained due to a differing lattice constant in the SiGe layer.
Further methods use mechanical stress induced by neighboring structures being densified by outgassing volatile components after deposition or by neighboring structures incorporating material from a gas-phase after solidification.
A general need exists to control charge carrier mobilities in silicon based devices by inducing strain into a silicon substrate.